Astrophysics (Index)About

Milky Way

(our galaxy)

The Milky Way is a spiral galaxy in which we reside. To us, it appears as a glowing band within the night sky, which if tracked around the whole celestial sphere is seen to form a ring around us, our view of a disk-shaped region of stars within which we are embedded. The galaxy is on the order of 100,000 light-years in diameter, about 1000 light-years in thickness and has 200-400 billion stars. Its mass is about a trillion solar masses. The solar system is about half way between its center and its edge. It is the second largest galaxy in the Local Group, the largest being Andromeda. An orbit of the Sun around the galaxy lasts in the range of 225-250 million years (i.e., the galactic period aka galactic year or cosmic year). The Milky Way's oldest stars are about 13 billion years old.

The Milky Way is naturally a target for up-close study of a galaxy, specifically, a disk galaxy. A stellar population classification of Milky Way stars based upon metallicity measures and location divides them into Population I stars, in the bulge and globular clusters with low metallicity, and Population II stars in the disk and spiral arms with higher metallicity. Of the latter group, location, kinematics and metallicity distinguish a thick disk at the lower end of the Population II metallicity scale and a thin disk at the higher end. Metallicity is presumed to grow with succeeding generations of stars, the metals being formed by stellar fusion and supernovae, the metals spread by the latter and by stellar wind, so older stars, necessarily leftovers from earlier generations, have lower metallicity. The Sun has a high metallicity but not the highest, falling in the middle of the thin disk's range. Stellar associations, the leftovers from recent star formation, can have higher.

(galaxy,Local Group,local)
Further reading:

Referenced by pages:
anomalous microwave emission (AME)
astronomical quantities
Balmer jump (BJ)
blind survey
Canis Major Dwarf Galaxy
carbon (C)
cosmic background radiation (CBR)
cosmic gamma ray background (CGB)
cosmic infrared background (CIB)
CMB anisotropies
cosmic optical background (COB)
cosmic distance ladder
cosmic dust
cosmic rays (CR)
Council of Giants
cosmic X-ray background (CXB)
dark matter halo
data cube
diffuse emission
disk galaxy
dispersion measure (DM)
distance modulus (μ)
Deep Underground Neutrino Experiment (DUNE)
dwarf galaxy
Event Horizon Telescope (EHT)
extragalactic astronomy
flux-weighted gravity-luminosity relationship (FGLR)
field galaxy
foreground subtraction
frame of reference
fast radio burst (FRB)
galactic archaeology
galactic astronomy
galactic binary
galactic bulge
galactic center
galactic disk
galactic electron density
galactic halo
galactic north
galactic plane
galactic worm (GW)
galaxy age determination
galaxy cluster (CL)
galaxy group
galaxy main sequence
Galactic All-sky Survey (GASS)
Green Bank Telescope (GBT)
G-dwarf problem
giant elliptical galaxy
globular cluster (GC)
Atlas of Galactic Nebulae (GN)
Galactic O Star Catalog (GOSC)
Gould's Belt
Great Debate
H3 Survey (H3)
Hα survey
hierarchical assembly of galaxies
high-velocity star
hot DOG
Hubble Ultra-Deep Field (HUDF)
high-velocity cloud (HVC)
hypervelocity star (HVS)
IC 342
inside-out growth
intensity mapping
intergalactic dust
interstellar magnetic field (ISMF)
jansky (Jy)
Kapteyn universe
kinematic distance
Laniakea Supercluster
luminous blue variable (LBV)
Large Magellanic Cloud (LMC)
Local Bubble
Local Group (LG)
Local Sheet
Lockman hole
Case-Hamburg Survey (LS)
local standard of rest (LSR)
luminosity density
luminosity distance (dL)
Local Volume (LV)
Andromeda (M31)
Triangulum Galaxy (M33)
MACHO Project
Magellanic clouds (MC)
Magellanic Stream
magnetic field
metallicity (Z)
Milky Way subgroup
Monoceros Ring
solar mass (MSun)
multiplicity fraction
Milky Way chemical evolution
N-body problem
NASA/IPAC Extragalactic Database (NED)
neutrino (ν)
nova (N)
Omega Centauri
Oort constants
open cluster (OC)
Orphan stream
oxygen (O)
physical field
Pisces-Cetus Supercluster Complex
primordial gravitational waves
radial velocity (RV)
rare designator prefixes
red dwarf
rotation curve
rotating radio transient (RRAT)
RR Lyrae variable (RRL)
Sag A*
Sagittarius Dwarf Elliptical Galaxy (Sgr dE)
satellite galaxy
satellite plane problem
Schwarzschild radius (RS)
Scutum-Centaurus Arm
Sloan Digital Sky Survey (SDSS)
star formation history (SFH)
SGR J1745-2900
supermassive black hole (SMBH)
Small Magellanic Cloud (SMC)
Smith Cloud
Kepler's Supernova
solar apex
solar neighborhood
Soltan argument
spectral line
spinning dust emission
spiral arm
spiral galaxy
Spitzer Space Telescope (SST)
starburst galaxy
stellar association
stellar-mass black hole
stellar distance determination
stellar kinematics
stellar population
stellar stream
thermal dust emission
21-cm line
Triangulum II (Tri II)
Two Micron All-sky Survey (2MASS)
ultra-faint dwarf galaxy (UFD)
Ursa Major II Dwarf
velocity-metallicity relation
Virgo Cluster
Virgo Stellar Stream
Westerhout Radio Survey (W)
wind-momentum luminosity relationship (WLR)
Wolf-Rayet star
X-ray luminosity function (XLF)
zone of avoidance (ZOA)